Tumor necrosis factor alpha (TNF.alpha.) is a potent cytokine that is released from many cell types, particularly, macrophages and monocytes. TNF.alpha. also exists in a cell-membrane bound, higher molecular weight form on cells, and this form also appears to mediate a variety of biological effects. TNF.alpha. is thought to have few roles in normal development and physiology; however, it exerts harmful and destructive effects on many tissues in many disease states (Tracey et al, Ann. Rev. Med. 45:491 (1994)). Disease states in which TNF.alpha. has been shown to exert a major pathogenetic role include septic shock syndrome, cancer cachexia, rheumatoid arthritis, etc. Many investigators and pharmaceutical companies are actively investigating agents and potential drugs that can block TNF.alpha. effects, either by blocking its synthesis or interfering with its binding to its surface receptors.
One example of this approach is the use of monoclonal antibodies to TNF.alpha.. These have been used in animal models of human disease, and in human conditions such as rheumatoid arthritis (Arend et al, Arthritis and Rheumatism 38:151 (1995)). There is no question that these antibodies temporarily relieve some of the signs and symptoms of this disease in man. However, their potential widespread use is compromised by many factors, especially the fact that they seem to be only temporarily (ie, a few months) effective. Other drawbacks include expense, the need for parenteral administration, the likelihood that anti-idotype antibodies will develop, etc.
The present invention relates to a novel approach to the treatment of diseases the effects of which are mediated, at least in part, through TNF.alpha.. This approach involves the protein tristetraprolin (TTP) and nucleic acid sequences encoding same.
TTP (Lai et al, J. Biol. Chem. 265:16556 (1990)), also known as Nup475 (DuBois et al, J. Biol. Chem. 265:19185 (1990)) and TIS11 (Varnum et al, Oncogene 4:119 (1989); Varnum et al, Mol. Cell. Biol. 11:1754 (1991)), is a widely distributed 33.6 kDa phosphoprotein encoded by the immediate-early response gene, Zfp-36 (Taylor et al, Nucl. Acids Res. 19:3454 (1991)). This gene has been mapped to chromosome 7 in the mouse, and the equivalent human gene, ZFP36, has been mapped to chromosome 19q 13.1 (Taylor et al, Nucl. Acids Res. 19:3454 (1991)). TTP is the prototype of a group of proteins containing two or more highly conserved putative zinc fingers of the CCCH class (Varnum et al, Mol. Cell. Biol. 11:1754 (1991); Taylor et al, Nucleic Acids Res. 19:3454 (1991); Gomperts et al, Oncogene 5:1081 (1990); Ma et al, Oncogene 9:3329 (1994)). In addition, the protein has been shown to bind Zn.sup.++ and has been localized to the cell nucleus in mouse fibroblasts (DuBois et al, J. Biol. Chem. 265:19185 (1990)), suggesting that it may be a transcription factor. Serum or other mitogen stimulation of quiescent fibroblasts causes rapid serine phosphorylation and nuclear to cytosolic translocation of TTP (Taylor et al, J. Biol. Chem. 270:13341 (1995); Taylor et al, Mol. Endocrinol. 10:140 (1996)), both of which are likely to modulate its function in cells.
In the adult mouse, TTP mRNA is highly expressed in lung, intestine, lymph node, spleen, and thymus, with lower expression in adipose tissue, kidney, and liver, and negligible expression in skeletal muscle and brain (Lai et al, J. Biol. Chem. 265:16556 (1990); DuBois et al, J. Biol. Chem. 265:19185 (1990)). In the thymus, TTP mRNA is highly expressed in both cortical and medullary thymocytes, while in the spleen, it is highly expressed in B and T lymphocytes within the white pulp, and is expressed at somewhat lower levels in the myeloid cells of the red pulp and endothelial cells of the high endothelial venules. In addition, TTP is constitutively expressed in several types of blood cells, particularly neutrophils, macrophages and B and T lymphocytes. The function of TTP in normal vertebrate physiology, however, was heretofore unknown.